In a healthy shoulder, the proximal humerus is generally ball-shaped, and articulates within a socket formed by the scapula, called the glenoid, to form the shoulder joint. Some implant systems for the total replacement of the shoulder joint generally replicate the natural anatomy of the shoulder. Such implant systems can include a humeral component having a stem that fits within the humeral canal, and an articulating head that articulates within the socket of a glenoid component implanted within the glenoid of the scapula.
Reverse-type shoulder implant systems have been developed in which the conventional ball-and-socket configuration that replicates the natural anatomy of the shoulder is reversed, such that a concave recessed articulating component is provided at the proximal end of the humeral component that articulates against a convex portion of a glenosphere of a glenoid component. For example, U.S. Pat. Nos. 7,854,768 and 7,959,680 discuss reverse shoulder systems.
In such reverse shoulder surgeries, implant components are installed on the glenoid portion of the scapula (i.e., shoulder blade) to replicate the shoulder joint. When an implant is installed on the scapula, it is commonly installed in the glenoid cavity, also known as the glenoid or glenoid fossa. The glenoid is a cavity that receives the head of the humerus in an anatomical shoulder. When an implant is used with the glenoid, the base of the implant is located within the glenoid, and could be secured thereto by fasteners such as screws, or using cement and/or fixation peg or keel.
One of the challenges when installing an implant in the glenoid relates to the positioning of implant. Due to the presence of ligaments and like soft tissue, the positioning of the implant must be planned to replicate as much as possible the normal bio-mechanical movements of the humerus relative to the scapula. Another challenge relates to the positioning of the fasteners that secure the implant to the scapula. Indeed, the scapula is relatively thin, and is surrounded by soft tissue. In order for the implant to be solidly secured to the scapula, the screws must be deep enough within the bone material. However, unless desired by the surgeon, the screws must not pierce through the bone surface so as not to damage soft tissue, such as nerves ligaments, tendons, etc.
Patient specific instrumentation (hereinafter “PSI”) pertains to the creation of instruments that are made specifically for the patient. PSI are typically manufactured from data using imagery to model bone geometry. Therefore, PSI have surfaces that may contact the bone in a predictable way as such contact surfaces are specifically manufactured to match the surface of a bone. It would therefore be desirable to use PSI technology in shoulder surgery.